sctp_inet6addr_event deletes 'addr' from 'local_addr_list' when setting
netdev down, but it is possible to delete the incorrect entry (match
the first one with the same ipaddr, but the different 'ifindex'), if
there are some netdevs with the same 'local-link' ipaddr added already.
It should delete the entry depending on 'sin6_addr' and 'sin6_scope_id'
both. otherwise, the endpoint will call 'sctp_sf_ootb' if it can't find
the according association when receives 'heartbeat', and finally will
reply 'abort'.

For example:
1.when linux startup
the entries in local_addr_list:
ifindex:35 addr:fe80::40:43ff:fe80:0 (eths0.201)
ifindex:36 addr:fe80::40:43ff:fe80:0 (eths0.209)
ifindex:37 addr:fe80::40:43ff:fe80:0 (eths0.210)

the route table:
local fe80::40:43ff:fe80:0 dev eths0.201
local fe80::40:43ff:fe80:0 dev eths0.209
local fe80::40:43ff:fe80:0 dev eths0.210

2.after 'ifconfig eths0.209 down'
the entries in local_addr_list:
ifindex:36 addr:fe80::40:43ff:fe80:0 (eths0.209)
ifindex:37 addr:fe80::40:43ff:fe80:0 (eths0.210)

the route table:
local fe80::40:43ff:fe80:0 dev eths0.201
local fe80::40:43ff:fe80:0 dev eths0.210

3.asoc not found for src:[fe80::40:43ff:fe80:0]:37381 dst:[:1]:53335
::1->fe80::40:43ff:fe80:0 HEARTBEAT
fe80::40:43ff:fe80:0->::1 ABORT
Signed-off-by: Chen Shen <peterchenshen@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>